I am now making plastic guards and clear plastic sets for some machines -
mostly those that I own, or those of friends. For the guards, I am using .060
PETG. PETG is a very tough plastic, but has a soft surface that marks easily.
the material will also yellow over time.

For clear plastics, I am working in .090 acrylic, in four grades. All three
grades have superb transparency and optical characteristics. They are also
brittle to a certain degree, the tradeoff for a hard surface. The ball doesn't
pose much of a threat, but the user of the machine can break them by bending
them too far, or by overtightening screws (which will cause crazing).

So - don't overtighten, and don't try to pull the acrylics around, and all
will be fine.

Cell
cast acrylic has the hardest surface of just about any uncoated
transparent plastic, and is notably clearer than PETG or polycarbonate.
It is also the strongest, stiffest acrylic. It has a medium edge
quality. The AFM sample to the right is cell cast acrylic, the
clear support is extruded acrylic.

Extruded acrylic is close to cell cast in physical properties;
it also takes a superb edge finish when cut with the laser, as you can
see on the edge of the support.

Impact
modified acrylic has the softest surface (but still much harder than
PETG or polycarbonate). This appears to be what people describe as
"acrylic polycarbonate". It is more flexible than the standard grades,
and about twice as resistant to impact. The edge finish is less
attractive than that of extruded acrylic. The washer on the right is cut
from impact modified acrylic, the support from extruded acrylic.

The
fourth grade is an abrasion resistant acrylic in 1/8" thickness. This
material is extruded, and takes a fine polish on the edges. It has a
silicon-based surface coating that resists marring - and should reduce
ball trails.

here you see a triangle I made for my MM ramps (top). The bottom
triangle is made from PETG. You can see the scruffy surface and cloudy
edges. These marks don't polish out, they have to be flamed.

One piece of trivia is that you cannot buy ramps in the U.S. with
these plastic triangles. This is because of U.S. patent
5,899,454. This patent describes a ramp very similar to the
ones used in Medieval Madness (the actual game uses the triangles the
other way around from the patent, which is very odd). Therefore, it is
illegal to make complete ramps or ramp kits unless you have a license
from the patent holder, Illinois Pinball. I'll be making these available
as part of a shop-out clears kit for MM.

Finally, here's a piece of PETG cut into a "shadow" for the
hunter-killer ship in T2.